Tuberous sclerosis complex (TSC) is an autosomal dominant neurogenetic disorder caused by defects in one of two genes, TSC1 or TSC2. Neurological symptoms (seizures, mental retardation, autistic features) are the most disabling problem and are related to characteristic brain lesions (cortical tubers). The severity of neurological disease can be quite varied, and this is not completely determined by genotype alone. In fact, there can be considerable variability in phenotype even within a single family, where all affected individuals have the same gene defect. The goal of this research is to understand the molecular basis of phenotypic variability in TSC. Several factors may affect phenotype in TSC including the specific gene mutation, random occurrence of second-hit somatic mutations, influence of other "modifying genes", or environmental factors. We hypothesize that an additional factor, allele-specific expression of the TSC genes, plays an important role in modifying disease severity. In this project, we shall test this by accomplishing the following specific aims: 1) Establish the prevalence of allelic-expression imbalance (AEI) of the TSC1 and TSC2 genes in the general population;(2) determine if the ratio of allelic expression is preserved across different tissues;and 3) relate severity of neurological disease in TSC patients (familial cases with multiple affected individuals) to the ratio of mutant : normal mRNA expression in peripheral blood leukocytes. We shall accomplish these aims by using coding region single nucleotide polymorphisms (SNPs) in an assay (SNaPshot assay) that will simultaneously allow us to distinguish and quantify the mRNAs expressed from the two alleles of each TSC gene. In this research proposal, we investigate the hypothesis that quantitative differences in the level of expression of the two alleles of each TSC gene, influences the phenotype in patients who carry a mutant gene. This is a novel idea, and may lead to the discovery of cis-acting regulatory polymorphisms that influence phenotype through this mechanism, and may eventually lead to a blood test that predicts disease severity. This research addresses an important problem for patients with TSC - genetic testing not being able to predict severity of disease. PUBLIC HEALTH RELEVANCE: One of the well documented issues in TSC (and in similar autosomal dominant neurocutaneous disorders such as NF1) is phenotypic variability. In most cases, defining the gene mutation does not allow us to predict disease severity. This proposal investigates a novel idea, that the severity of disease in patients with TSC is modulated by quantitative regulation of TSC1 and TSC2 gene expression. By relating allelic expression imbalance of TSC1 or TSC2 in blood samples to severity of neurological symptoms, we may be able to develop a blood test that might predict clinical severity. This will facilitate selection of TSC patients for earlier and more aggressive treatment protocols, especially as we develop novel drugs that target various aspects of the mTOR or Ras/MAPK signaling pathways. PUBLIC HEALTH RELEVANCE: One of the well documented issues in TSC (and in similar autosomal dominant neurocutaneous disorders such as NF1) is phenotypic variability. In most cases, defining the gene mutation does not allow us to predict disease severity. This proposal investigates a novel idea, that the severity of disease in patients with TSC is modulated by quantitative regulation of TSC1 and TSC2 gene expression. By relating allelic expression imbalance of TSC1 or TSC2 in blood samples to severity of neurological symptoms, we may be able to develop a blood test that might predict clinical severity. This will facilitate selection of TSC patients for earlier and more aggressive treatment protocols, especially as we develop novel drugs that target various aspects of the mTOR or Ras/MAPK signaling pathways.